As is known to all, air permeability and water vapor permeability are two critical aspects that affect the comfortability of shoes. The water vapor and sweat in the shoes can be taken away by the air exchange. The exchange of air, water vapor, and heat between the in-shoe microenvironment and the outside environment has been the subject of quite a few inventions. All the efforts are trying to improve these exchange and therefore to reduce the moist in the microenvironment inside shoes and to improve their comfortbility.
U.S. Pat. No. 6,508,015 disclosed a breathable outsole for footwear, in which the outsole has a two-layer structure. The two-layer structure contains an elastic and water vapor-permeable inner layer and an outer layer that covers less than 70% of the inner layer. The breathing activity of outsole is provided by the microporous structure of inner layer and the configuration of outer layer. The configuration of outer layer is such that the surface of inner layer available for water vapor exchange is restricted as little as possible. A microporous structure of insole is achieved, for example, by a sintered plastic.
U.S. Pat. No. 6,655,048 disclosed a breathable and waterproof sole for shoes, which comprises, at least along part of its extension, a lower waterproof component, which constitutes the tread; an upper component, with a supporting structure which has chambers which are connected to openings at least on the upper face and the edge; a membrane which is impermeable to water and vapor-permeable and externally surrounds at least the outward-facing regions of the upper component. The lower and upper components and the membrane are joined so as to form a seal at least in the regions where water infiltration is possible.
A vapor-permeable and waterproof sole for shoes was disclosed in U.S. Pat. No. 6,681,500, which comprising: a lower flat element made of shaped rubber-like material, which has a hollow upper region delimited by a border with air passage openings which extend laterally with respect to the ground resting plane; an upper element; a membrane made of waterproof and vapor-permeable material, which is interposed between said lower and upper element at said hollow region; said lower and upper elements and said membrane being joined hermetically in the perimetric regions of mutual contact.
U.S. Pat. No. 7,367,141 disclosed a waterproof and breathable sole for shoes, having a structure including a supporting layer which, at least in a preset macroportion, is made of net, felt, or other diffusely perforated material. A membrane made of a material that is impermeable to water and permeable to water vapor is associated above the supporting layer at least in the one preset macroportion made of net, felt or other diffusely perforated material, which it covers. A tread made of plastic material, with at least one through macroperforation at the at least one preset macroportion made of net, felt or other diffusely perforated material, is joined hermetically to the membrane and to the supporting layer at least at the perimeter of the at least one macroportion made of net, felt or other diffusely perforated material.
Although the above-mentioned soles have been commercially available for years and are able to provide the exchange of heat and water vapor between the in-shoe microenvironment and outside environment, the problem for better air permeability still remains in the shoes with these kinds of soles. In the case of the above soles, the functions of air, water vapor, and heat exchange to outside environment cannot be realized with the desired rate and hence the comfortability is still limited due to the membrane water impermeable materials and the limited space for air and water vapor exchange. These waterproof membrane have the air permeability of 300.000 kPa·s·m−1 to 700.000 kPa·s·m−1.